I think you have the wrong idea. I'm not GOING to spend £8k on it am I? I may spend the £1k on a new ecu, giving me a better car than if I spent £1k on a new car.
If you're going to spend a Grand, you sell/trade your non fully functioning car for £2000 and put that Grand to make it £3000 purchase price
WHY do you keep forgetting that your half working car DOES have a value?